Method for preserving fresh marine products with use of a deoxidant

ABSTRACT

A preserving agent for fresh marine product comprising (A) at least one salt selected from the group consisting of chlorates, chlorites and hypochlorites; (B) iron powder; and (C) at least one oxide selected from the group consisting of ferric oxide, cobalt oxide, nickel oxide, zinc oxide, titanium oxide, zirconium oxide, germanium oxide, copper oxide, silver oxide and manganese oxide and a method of preserving fresh marine products using the preserving agent; 
     a method for preserving crustaceans which comprises putting crustaceans into a container, covering the container, and quickly adjusting the oxygen concentration within the container to 0.5 to 5 vol %; and 
     a container for preserving fresh marine products in the state of being packed with ice, comprising a receptacle in which said fresh marine products are placed and which has at the bottom thereof at least one hole for draining water therethrough, a removable or hinged lid, and a water-permeable material which is placed so as to drain water therethrough and prevent air outside said container from entering therethrough into said container, and a method of preserving fresh marine products using the container are disclosed.

This application is a divisional of application Ser. No. 433,367 filedNov. 8, 1989.

BACKGROUND OF THE INVENTION

The present invention relates to a preserving agent, a method and acontainer for maintaining the freshness of fresh marine products andparticularly, preventing the change of color thereof when they are keptin cold storage in the raw state.

The color of the body of a marine product generally changes rapidlyafter the death. Since the change of color is related to the loss offreshness and leads to the degradation of the commercial value,prevention of change of color of marine products is an important problemto be solved. Change of color occurs in various marine products. Theyinclude crustaceans such as lobster, shrimp, prawn and crab, what iscalled red body fishes such as red sea bream (Madai), red rockfish(Menuke), bluefin searobin (Hobo) and alfonsino (Kinmedai), what iscalled white meat fishes such as cod and flatfish, tuna meat, bonitomeat, sardine, mackerel, squid, cuttlefish and scallop.

For example, the colors of raw crustaceans such as lobster, shrimp,prawn and crab are apt to be changed into blackish colors soon afterfishing, whereby the commercial value is greatly lowered. The portionsat which the color is changed into blackish color is mainly the headportion in the case of lobster, shrimp or prawn and leg joint portionsin the case of crab. The color is changed into blackish color becausetyrosine in the body finally produces melanine polymer by the action ofan oxidizing enzyme tyrosinase and the like in the presence of oxygen.It is therefore possible to prevent the color from changing intoblackish color either by inactivating the enzyme by heating or bydepressing the action of the enzyme by freezing. In the case ofdistributing crustaceans in the raw state, however, these methods cannotnaturally be adopted. As a method of preventing the color of crustaceansfrom changing into blackish color in the raw state, if it is assumed tobe one, a method of immersing crustaceans in a solution of an organicacid such as citric acid by utilizing the fact that tyrosinase isinactivated at a pH of not more than 5 is known. A method of immersingcrustaceans in an aqueous sodium hydrogensulfite solution is also known.Both of these methods have insufficient effects and particularly thelatter method has a problem in the regulation of residual SO₂. In fact,it is the present state of art that there is no effective method otherthan shortening the distribution period from fishermen to consumers.

The red color of red fishes such as red sea bream is derived from redcarotenoid pigments. Carotenoids are easily oxidized, thereby fading incolor. As a countermeasure, red sea bream is immersed in a solution ofreductive sodium ascorbate or an antioxidant is added to red sea bream.However, treatment with chemicals is sometimes undesirable and theeffect thereof cannot be said sufficient.

In some marine products such as tuna meat, myoglobin which presentsscarlet color is oxidized and changed into methomyoglobin which presentsbrown color. Fishes such as sardine and mackerel change the color intobrownish color by browned substances which are formed when the lipid inthe fish meat is oxidized.

Since the change of color in fresh marine products is often caused byoxidation, as described above, use of a deoxidant has been proposed.However, not only low deoxidizing ability of conventional deoxidants ata low temperature under the cold-storage conditions but also aconventional method of merely removing oxygen still has a problem fromthe point of view of the total maintenance of the freshness although thechange of color can be prevented. Thus, the improvement on maintainingthe freshness of marine products has been demanded.

As described above, in the case of distributing fresh marine products inthe raw state, the limitation of time for maintaining the freshness isone or two days even they are kept in cold storage, and if the timeexceeds the limitation, the color changes. Therefore, if there is sometrouble in transportation on the way, the commercial value is greatlylowered. Transportation from remote districts which require a long timeis often impossible in the present state of art.

Accordingly, it is an object of the present invention to solve theabove-described problems in the prior art and to provide a preservingagent, a method and a container for preventing the freshness of freshmarine products from lowering and, in particular, preventing the changeof color of the body thereof.

SUMMARY OF THE INVENTION

In a first aspect of the present invention, there is provided apreserving agent for fresh marine products comprising (A) at least onesalt selected from the group consisting of chlorates, chlorites andhypochlorites; (B) iron powder; and (C) at least one oxide selected fromthe group consisting of ferric oxide, cobalt oxide, nickel oxide, zincoxide, titanium oxide, zirconium oxide, germanium oxide, copper oxide,silver oxide and manganese oxide and a method (I) for preserving freshmarine products using the preserving agent.

In a second aspect of the present invention, there is provided a method(II) for preserving fresh crustaceans which comprises the steps ofputting the fresh curstaceans into a container, sealing up the containeror covering the container with a lid, and quickly adjusting the oxygenconcentration within the container to 0.5 to 5 vol %.

In a third aspect of the present invention, there is provided acontainer for preserving fresh marine products, which can be used in theabove two methods and a method for preserving fresh marine product byusing the container.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a sectional view of one example of a container for preservingfresh marine products according to the present invention.

In FIG. 1, 1 is a container, 2 is a hole for draining watertherethrough, 3 is unwoven cloth, 4 is ice, 5 and 7 are partitions, 6 isfresh marine products to be preserved and 8 is a deoxidant.

DETAILED DESCRIPTION OF THE INVENTION

Chlorates, chlorites and hypochlorites used in the present invention arenot restricted, but the respective alkali metal salts and alkaline earthmetal salts are preferable. The ratio of the salt (A) to the iron powder(B) is not restricted, but it is preferably 1 to 50 parts by weight, andmore preferably 2 to 30 parts by weight of the salt (A) based on 100parts by weight of the iron powder (B).

The ratio of at least one oxide (C) selected from the group consistingof ferric oxide, cobalt oxide, nickel oxide, zinc oxide, titanium oxide,zirconium oxide, germanium oxide, copper oxide, silver oxide andmanganese oxide to the iron powder (B) is also not restricted, butpreferably 1 to 90 parts by weight, and more preferably 2 to 60 parts byweight based on 100 parts by weight of (B) the iron powder.

A process for preparing the preserving agent of the present invention isnot specified, but a method of uniformly mixing the ingredient in thepowdery state is simple and preferable.

The preserving agent of the present invention can be carried by or mixedwith a porous carrier ordinarily used. Examples of preferable carriersare silica, alumina, silica alumina, zeolite, talc, diatomaceous earth,Kanuma soil, clay minerals, activated clay and active carbon, but thecarrier is not restricted thereto.

The ratio of carrier is not restricted, but preferably 0 to 500 parts byweight, and more preferably 5 to 200 parts by weight based on 100 partsby weight of (B) the iron powder.

The deoxidizing rate of the preserving agent of the present invention isaccelerated in the presence of water like other deoxidants containingiron powder as the main ingredient. In preserving fresh marine products,there is usually sufficient water in a container, and in this case nospecial care for adding water is necessary. However, in some cases, itis possible to use the above-described carrier or a water-absorbingpolymer containing water.

The preserving agent of the present invention is different fromconventional deoxidants in that it has an excellent deoxidizing activityat a low temperature, in that it has also total freshness maintainingeffect on fresh marine products such as color change preventive effectand rot preventing effect and mold inhibiting effect, and in that it hascolor change preventive effect even if the cause of color change is notoxidation.

In the method (I) for preserving fresh marine products, fresh marineproducts are put into a container together with the preserving agent ofthe present invention and the container is sealed up or covered with alid for preservation. The preserving agent is generally put into a baghaving gas-permeability. The amount of preserving agent used is notrestricted but is preferably so controlled that the oxygen concentrationin the preserving atmosphere is maintained in the range of 0.5 to 5vol%, preferably 0.5 to 3 vol %. If the oxygen concentration exceedsthis range, complete prevention of color change is difficult, while ifit is less than 0.5 vol%, anaerobic bacteria may propagate.

In addition, since the rate of color change is high, as described above,it is preferable not only to control the oxygen concentration rangewithin the above-described range but also to adjust the oxygenconcentration to the range as soon as possible. The time required toreduce the oxygen concentration to the above range, which is differentdepending upon marine products, cannot be determined indiscriminatelybut not more than 24 hours is appropriate.

The container used in the method (I) is not specified so long as it hasa high airtightness. Polystyrene foam boxes may generally be used andgeneral plastic bags of barrier films or plastic containers are alsousable.

The temperature for preserving fresh marine products by using thepreserving agent of the present invention is preferably as low aspossible unless they freeze. Cooling with ice or cold storage in arefrigerator can generally provide preferable results. This is becausethe preserving agent of the present invention is aimed at preservingmarine products in the raw state, but it goes without saying that thepreserving agent of the present invention is adaptable under freezingand a sufficient effect can be expected.

The preserving agent of the present invention is effective for all freshmarine products in which change of color occurs. For example, thepreserving agent is effective for preventing the colors of crustaceanssuch as lobster, shrimp, prawn and crab and red fishes such as red seabream, red rockfish, bluefin searobin and alfonsino, etc. from changinginto blackish colors or fading, preventing the change in color of tunameat, yellowtail meat, etc., preventing browning of white meat fishes,preventing the change in color of a sardine, mackerel, etc., preventingbrowning of scallop, maintaining the qualities of sea urchin, pollackroe, etc., and preventing the change in color of squid and cuttlefishbut the effects are not restricted thereto. In addition, the preservingagent of the present invention is effective for not only the preventionof change of color but also the maintenance of freshness by preventingrotting or the like. In this case, the marine products to be preservedis not restricted to marine products the colors of which are apt tochange.

The method (II) for preserving fresh crustaceans of the presentinvention comprises the steps of putting fresh crustaceans into acontainer, sealing up the container or covering the container with alid, and quickly adjusting the oxygen concentration within the containerto 0.5 to 5 vol%, preferably 0.5 to 3 vol%. The term "quickly" heremeans within 24 hours, preferably within 16 hours.

If the oxygen concentration exceeds this range, it is difficult tocompletely prevent the color of fresh crustaceans from changing intoblackish color, while if it is less than this range, anaerobic bacteriamay propagate. In addition, since the rate of change of color intoblackish color is high, as described above, it is preferable not only tocontrol the oxygen concentration range but also to shorten the time foradjusting the oxygen concentration to the above-mentioned range as muchas possible. As mentioned above, the time required to reduce the oxygenconcentration to the above range is not more than 24 hours, preferablynot more than 16 hours.

The oxygen concentration is preferably adjusted by using a deoxidant. Inorder to further enhance the effect of the method (II) of the presentinvention, preservation at a low temperature is preferable, and it istherefore necessary to select a deoxidant having a sufficientdeoxidizing activity even at a low temperature. From this viewpoint, acomposition comprising (A) at least one salt selected from the groupconsisting of chlorates, chlorites and hypochlorites and (B) iron powderwill be cited as an example of an especially preferred deoxidant.Chlorates, chlorites and hypochlorites are not restricted, but therespective alkali metal salts and alkaline earth metal salts arepreferable.

The ratio of at least one salt (A) selected from the group consisting ofchlorates, chlorites and hypochlorites to the iron powder (B) is notrestricted, but it is preferably 1 to 50 parts by weight, and morepreferably 2 to 30 parts by weight based on 100 parts by weight of theiron powder (B).

As an especially preferable deoxidant, the above-described preservingagent for fresh marine products can be cited.

The deoxidant can be carried by or mixed with a porous carrier, asdescribed above.

The deoxidizing rate of deoxidants is accelerated in the presence ofwater. In preserving crustaceans, there is usually sufficient water in acontainer, and in this case no special care for adding water isnecessary. However, in some cases, it is possible to use theabove-described carrier or a water-absorbing polymer containing water.When a deoxidant is used, it is generally put into a bag havinggas-permeability. Since the deoxidants exemplified above not only areexcellent in deoxidizing activity at a low temperature but also haveeffect for preventing fading of the color of crustaceans and preventingrotting, they are especially preferable as the deoxidant used in themethod (II) of the present invention.

Crustaceans are exemplified by various shrimps, prawn, lobsters andcrabs.

The container used in the method (II) of the present invention is notspecified so long as it has a high airtightness. Polystyrene foam boxesmay generally be used and general plastic bags of barrier films orplastic containers are also usable.

The preserving temperature is not specified but is actually preferablyas low as possible unless crustaceans freeze. Cooling with ice or coldstorage in a refrigerator can generally provide preferable results. Thisis because the method (II) of the present invention is aimed atpreserving crustaceans in the raw state, but it goes without saying thatthis method is applicable under freezing and a sufficient effect can beexpected.

According to the method (II) of the present invention, it is possible toprevent change of color in fresh crustaceans such as lobster, shrimp,prawn and crab, and avoid the degeneration of the quality thereof.

The present invention further relates to a container for preservingfresh marine products, which can be used in the methods (I) and (II).

In the case of transporting or storing fresh marine products in thestate of being packed with ice, containers such as polystyrene foamboxes and water-proof corrugated cardboard boxes are used. In this case,holes are generally made in the bottom of a container so that the waterfrom melted ice is drained therethrough. However, as described above,color of change in fresh marine products is mostly caused by oxidationdue to oxygen in air. In order to prevent the oxidation, a method ofreplacing oxygen in the container with another gas or a method ofremoving the oxygen from the container may be considered. Theabove-described holes obstruct these methods because air passes throughthose holes. On the other hand, if the container without any hole isused the fresh marine products are soaked in the water from melted ice,whereby the freshness is lowered.

As a result of various studies on a container for transporting orstoring fresh marine products in the state of being packed with icewhich can drain water without letting external air into the container,the present inventors have found that such a container can be obtainedby making holes for draining water therethrough in the bottom of thecontainer and covering the inner or outer end of the hole or filling thehole with a water-permeable material such as paper, cloth and unwovencloth. This is because a water-permeable material is permeable to water,but once it is wet with water, it becomes impermeable to gas such asair. When fresh marine products are actually put into a container of thepresent invention together with crushed ice and stored in a low-oxygenstate by using a deoxidant, the water from melted ice is drained out ofthe container, and the low-oxygen state is held, thereby maintaining thefreshness of the fresh marine products. The container of the presentinvention has been achieved on the basis of this finding.

That is, the present invention further relates to a container for use inpreserving fresh marine products packed with ice, which is provided withholes for draining water therethrough made in the bottom thereof and theinner or outer end of the hole is covered with or the hole is filledwith a water-permeable material, and a method for preserving freshmarine products comprising the steps of packing fresh marine productswith ice in the container together with a deoxidant and covering thecontainer with a lid.

There is no restriction in material for the container of the presentinvention so long as it has a barrier characteristic which is capable ofmaintaining a low-oxygen state. From the point of view of practical use,polystyrene foam boxes with a removable lid and water-proof corrugatedcardboard boxes having a removable or hinged lid are preferable. Atleast one hole is formed in the bottom of the container and the inner orouter end of the hole is covered with or the hole is filled with awater-permeable material. The shape of the hole is not restricted so faras the purpose of the present invention can be achieved, and may becylindrical, prismatic or convergent. The dimension or hole isappropriately selected based on the bottom area of the container.

The water-permeable material in the present invention means a materialwhich is permeable to water, but which prevents the gas-permeabilityonce it is wet with water. Any material having this nature is usable.Examples of a preferable material are water-proof paper, cloth orunwoven cloth. The water-permeable material may be placed on one of orboth the ends of the hole or may be filled in the hole in a manner thatthe placed or filled material do not come out or move duringpreservation or storage.

The container of the present invention is aimed at for preserving freshmarine products packed in ice in a low-oxygen state. When fresh marineproducts are preserved, they are packed with ice in the container, adeoxidant (preserving agent for fresh marine products) is further putinto the container, and the container is covered with a lid.

The present invention will be explained in more detail with thefollowing non-limitative examples. "Part" in the examples represents apart by weight.

EXAMPLE 1

Live boreal prawn (Amaebi) caught off the coast of Noto were soaked in alarge amount of iced water and allowed to stand for about 4 hours. 10 ofthose boreal prawns were sealed in an OPP film bag of 50 μm in thicknesstogether with a water-repellent and gas-permeable bag filled with 10 gof a composition (preserving agent) comprising 300 parts of iron powder,30 parts of calcium hypochlorite, 20 parts of ferric oxide and 50 partsof active carbon. The sealed package was preserved at 0° C.. Even after4 days, the color was not changed into blackish color at the headportion and the tail portion in any boreal prawns. The pink color of thebody was also maintained. In contrast, in all the boreal prawnspreserved in the same way except that the preserving agent was not putinto the OPP film bag, the colors were changed into blackish colors atthe head and the tail portions, and the pink colors of the bodies fadedand became yellowish as after whole 2 days. The oxygen concentration inthe bag (OPP film bag) containing the preserving agent reduced to 1.7%in 16 hours, and substantially the same level was maintained for wholestoring period. In contrast, the oxygen concentration in the bag (OPPfilm bag) without the preserving agent was 15% even after 4 days.

EXAMPLES 2 and 3

The same tests as in Example 1 were carried out except that sodiumchlorite and sodium chlorate were respectively used in place of calciumhypochlorite. In each case, the color was not changed into blackishcolor at the head portion and the tail portion in any boreal prawns. Thepink color of the body was also maintained. The oxygen concentration inthe bag (OPP film bag) reduced to 1.8% in 16 hours, and thereafter wasmaintained at about 1.5%.

EXAMPLE 4

One red sea bream (Madai) was sealed in a polyethylene film bag of 50 μmin thickness together with a gas-permeable bag filled with 10 g of apreserving agent comprising 300 parts of iron powder, 30 parts ofcalcium hypochlorite, 20 parts of cobalt oxide and 50 parts of activecarbon. The sealed package was preserved at 0° C. Even after 1 week, nochange was observed in the color of the body and the freshness waswholly maintained.

EXAMPLES 5 to 12

Tests of preserving a red sea bream were carried out in the same way asin Example 4 except that nickel oxide, zinc oxide, titanium oxide,zirconium oxide, germanium oxide, copper oxide, silver oxide andmanganese oxide, respectively, were used in place of cobalt oxide. Ineach of Examples, even after 1 week, no change was observed in the colorof the body and the freshness was wholly maintained.

EXAMPLE 13

200 g of fillet of raw tuna meat was sealed in a polyethylene film bagof 50 μm in thickness together with a gas-permeable bag filled with 10 gof a preserving agent comprising 300 parts of iron powder, 20 parts ofsodium hypochlorite, 15 parts of zinc oxide, 15 parts of ferric oxideand 50 parts of active carbon. The sealed package was preserved at 5°°C.Even after 3 days, the scarlet color was maintained and no dripping wasobserved. In contrast, in a piece of raw tuna meat which was preservedwithout the preserving agent, the color of the body faded with partthereof being changed into a greenish color, and dripping was observed.

EXAMPLE 14

20 fresh sardines were packed with ice in a polystyrene foam box(FIG. 1) together with a gas-permeable bag filled with 40 g of thepreserving agent obtained in Example 13 and covered the box with a lid.The box was preserved at 5° C. Even after 5 days, no change was observedin the color of the body and the freshness was wholly maintained.

EXAMPLE 15

Live boreal prawns caught off the coast of Noto were immediately killedand 10 of them were sealed in an OPP film bag of 50 m in thicknesstogether with a gas-permeable bag filled with 10 g of a deoxidant(preserving agent) comprising 300 parts of iron powder, 30 parts ofcalcium hypochlorite, 20 parts of zinc oxide and 50 parts of activecarbon. The sealed package was preserved at 0° C.. Even after 4 days,the color was not changed into blackish color at the head portion andthe tail portion in almost any boreal prawns. The pink color of the bodywas also maintained. In contrast, in all the boreal prawns preserved inthe same way except that the deoxidant was not put into the bag, thecolors were changed into blackish colors at the head and the tailportions, and the pink colors of the bodies faded and became yellowishafter 2 days. The oxygen concentration in the bag (OPP bag) containingthe deoxidant reduced to 1.5% in 16 hours, and substantially the sameconcentration even after 4 days. In contrast, the oxygen concentrationin the bag containing no deoxidant was 15% even after 4 days.

EXAMPLES 16 and 17

The same tests as in Example 15 were carried out except that sodiumchlorite and sodium chlorate were respectively used in place of calciumhypochlorite. In each Example, the color was not changed into blackishcolor at the head portion and the tail portion in any boreal prawns. Thepink color of the body was also maintained. The oxygen concentration inthe bag (OPP bag) reduced to 1.8% in 16 hours and was thereaftermaintained in the range of 1 to 1.5%.

EXAMPLE 18

10 fresh tiger prawns (Kurumaebi) were sealed in an OPP film bag of 50μm in thickness together with a gas-permeable bag filled with 10 g of adeoxidant comprising 300 parts of iron powder, 30 parts of calciumhypochlorite, 10 parts of ferric oxide, 10 parts of zinc oxide and 50parts of active carbon. The sealed package was preserved at 0° C. Evenafter 4 days, the color was not changed into blackish color at the headportion and the tail portion in any prawn. The color of the body wasalso not changed in almost any prawn. In contrast, in the prawnspreserved in the same way except that the deoxidant was not put into thebag, the colors were progressively changed into blackish colors at thehead portions, and the colors of the bodies became wholly blackish after2 days. The oxygen concentration in the bag (OPP bag) containing thedeoxidant reduced to about 2% in 16 hours, and substantially the sameeven after 4 days. In contrast, the oxygen concentration in the bagcontaining no deoxidant was 17% even after 2 days.

EXAMPLE 19

One fresh pacific snow crab (Zuwai-Kani) was packed in a polystyrenefoam box (FIG. 1) together with a gas-permeable bag filled with 20 g ofa deoxidant comprising 200 parts of iron powder, 30 parts of calciumhypochlorite and 70 parts of active carbon. The box was preserved at 0°C. Even after 5 days, no change was observed in the color of the bodyand the freshness was wholly maintained. During this time, the oxygenconcentration in the container (polystyrene foam box) reduced to about3% in 16 hours after the start of the test and was thereafter maintainedat 2 to 3%.

EXAMPLE 20

As shown in FIG. 1, at the four corners of the bottom of a polystyrenefoam box 1 with a lid having a dimension of 34 cm in length, 52 cm inwidth and 13 cm in height, holes 2 (1 cm in diameter) for draining watertherethrough were made. Polyester unwoven cloth 3 (Gurley permeability:10 sec/100 ml of air) was applied on the inner end of each hole toproduce a container for preserving fresh marine products. Crushed ice 4was packed in the container and a partition 5 was placed on the crushedice 4. 2.5 kg of fresh boreal prawns 6 caught on the day of the testwere arranged on the partition 5. Another partitions 7 was placed on theboreal prawns 6, which were covered with a gas-permeable bag filled with40 g of the deoxidant 8 used in Example 15. The container was coveredwith the lid to be preserved at 5° C. The oxygen concentration in thecontainer was reduced to the order of 2 % in 24 hours, and was graduallylowered until it became about 1% after 4 days. The low-oxygen state wasmaintained thereafter. During this time, the water from melted ice wasdrained out of the container through the unwoven cloth. The color of theboreal prawns was not changed into blackish color at the head portionand the tail portion after 6 days. The pink color of the body was alsomaintained. In contrast, in the boreal prawns preserved in the same wayexcept that the deoxidant was not used, the colors were changed intoblackish colors at the head and the tail portions after 2 days.

EXAMPLES 21 and 22

Containers for preserving fresh marine products were produced in thesame way as in Example 20 except that cotton cloth and filtering paperwere respectively used in place of the polyester unwoven cloth. As aresult of a similar test, a substantially the same result was obtainedin both cases.

EXAMPLE 23

A gas-permeable bag was filled with 20 g of a preserving agentcomprising 200 parts by weight of iron powder, 20 parts by weight ofcalcium hypochlorite, 10 parts by weight of zinc oxide, 10 parts byweight of ferric oxide, 60 parts by weight of active carbon and 200parts by weight of activated clay containing 20 parts by weight ofwater. Three trays loaded with 150 g of shucked sea urchin were sealedin an OPP film bag of 50 μm in thickness together with the preservingagent. The sealed package was preserved at 0° C. for 25 days. The freshstate was maintained without losing the original shape and putrid smell.In contrast, in the cases of shucked sea urchin which was preservedwithout the preserving agent, the original shape was wholly lost andthere was putrid smell.

EXAMPLE 24

The same preservation test was carried out as in Example 23 except that500 g of pollack roe was used in place of sea urchin and thepreservation temperature was changed to 5° C.. While the pollack roepreserved without the preserving agent produced a change of color andbad smell, the pollack roe preserved together with the preserving agentwas free from change of color and bad smell, and also had a good taste.

EXAMPLE 25

A gas-permeable bag was filled with 5 g of a preserving agent comprising300 parts by weight of iron powder, 20 parts by weight of calciumhypochlorite, 10 parts by weight of zinc oxide, 10 parts by weight offerric oxide, and 60 parts by weight of active carbon. 2 slices ofyellowtail meat were sealed in a nylon/polyethylene bag of 30 μm inthickness together with the preserving agent. The sealed package waspreserved at 0° C. for 2 days. While in the package without thepreserving agent, the change of color was remarkable on the surface ofthe meat, the fresh state of the meat was maintained in the packagecontaining the preserving agent.

EXAMPLE 26

Ice was packed in the polystyrene foam container shown in FIG. 1, and 2alfonsino were placed thereon. A gas-permeable bag filled with 20 g ofthe preserving agent used in Example 25 was further placed thereon. Thecontainer was covered with the lid and sealed with an adhesive tape. Thecontainer was preserved at 2° C. for 6 days. While the meat of fish waskept white and the viscera were firm in the container containing thepreserving agent, the color of the meat of fish changed into reddishcolor and the viscera lost the original shape, in other words, thefreshness was greatly lowered in the container without the preservingagent.

What is claimed is:
 1. A method for preserving fresh marine products,which comprises putting said fresh marine products and a preservingagent comprising (A) at least one salt selected from the groupconsisting of chlorates, chlorites and hypochlorites; (B) iron powder;and (C) at least one oxide selected from the group consisting of ferricoxide, cobalt oxide, nickel oxide, zinc oxide, titanium oxide, zirconiumoxide, germanium oxide, copper oxide, silver oxide and manganese oxide,into a container and adjusting the oxygen concentration within saidcontainer to the range of 0.5 to 5 vol %, the concentration beingmaintained in the range thereafter.
 2. The method for preserving freshmarine products according to claim 1, wherein the ratio of said (A), (B)and (C) is 1 to 50:100:1 to 90 by weight ratio.
 3. The method ofpreserving fresh marine products according to claim 1 or 2, wherein said(A) is calcium hypochlorite.
 4. The method for preserving fresh marineproducts according to claim 1 or 2, wherein said fresh marine productsare crustaleans or sea urchin.